PHOTOGRAPHIC CORRESPONDENCE. _History of Photographic Discovery._--Without entirely agreeing with the opinion expressed to us a few days since, by an eminent scholar and most original thinker, that photography was destined to change the face of the whole world; we have little doubt it is destined to produce some striking social effects. Its history is, therefore, an interesting one, and the following extract from a paper "On some early Experiments in Photography, being the substance of a Letter addressed to Robert Hunt, Esq., by the Rev. J. B. Reade, M.A., F.R.S.," from the _Philosophical Magazine_ for May, 1854, seems, in that point of view, so important, that we have transferred it to "N. & Q." "I may assume that you are already aware, from my letter to Mr. Brayley of March 9, 1839, and published in the _British Review_ for August, 1847, that the principal agents I employed, before Mr. Talbot's processes were known, were infusion of galls as an accelerator, and hyposulphite of soda as a fixer. "I have no doubt, though I have not a distinct recollection of the fact, that I was led to use the infusion of galls from my knowledge of the early experiments by Wedgwood. I was aware that he found _leather_ more sensitive than _paper_; and it is highly probable that the tanning process, which might cause the silver {525} solution to be more readily acted upon when applied to the leather, suggested my application of the tanning solution to paper. "In your own history of the photographic process," says Mr. Reade, addressing Mr. Hunt, "you say, 'the discovery of the extraordinary property of the gallic acid in increasing the sensibility of the iodide of silver was the most valuable of the numerous contributions which Mr. Talbot has made to the photographic art.' It is nevertheless true, as stated by Sir David Brewster, that 'the first public use of the infusion of nut-galls, which is an _essential element_ in Mr. Talbot's patented process, is due to Mr. Reade;' and in my letter to Mr. Brayley I attribute the sensitiveness of my process to the formation of a gallate or tannate of silver. I need scarcely say, that among various experiments I tried gallic and tannic acid in their pure state, both separately and mixed; but the colour of the pictures thus obtained with the solar microscope was at that time less pleasing to my eye, than the rich warm tone which the same acids produced when in their natural connexion with solutions of vegetable matter in the gall-nut. This organic combination, however, was more effective with the solar microscope than with the camera, though the lenses of my camera were five inches in diameter. It is probable enough that the richer tone was due to the greater energy of direct solar rays. In using the solar microscope, I employed a combination of lenses which produced a convergence of the luminous and photogenic rays, together with a dispersion of the calorific